Modern communications demand higher data rates and performance. Multiple input, multiple output (MIMO) antenna systems, also known as multiple-element antenna (MEA) systems, achieve greater spectral efficiency for allocated radio frequency (RF) channel bandwidths by utilizing space or antenna diversity at both the transmitter and the receiver, or in other cases, the transceiver.
In MIMO systems, each of a plurality of data streams is individually mapped and modulated before being precoded and transmitted by different physical antennas or effective antennas. The combined data streams are then received at multiple antennas of a receiver. At the receiver, each data stream is separated and extracted from the combined signal. This process is generally performed using a minimum mean squared error (MMSE) or MMSE-successive interference cancellation (SIC) algorithm.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, the base station transmits a Downlink (DL) grant to a subscriber station in a Physical Downlink Control Channel (PDCCH). Some frames later, the subscriber station transmits an Acknowledgement (ACK) or Negative Acknowledgement (NACK) to the base station.